* Alexander Duyck <alexander.h.du...@intel.com> wrote:
> This patch is meant to improve overall system performance when
> making use of the __phys_addr call on 64 bit x86 systems. To
> do this I have implemented several changes.
>
> First if CONFIG_DEBUG_VIRTUAL is not defined __phys_addr is
> made an inline, similar to how this is currently handled in 32
> bit. However in order to do this it is required to export
> phys_base so that it is available if __phys_addr is used in
> kernel modules.
>
> The second change was to streamline the code by making use of
> the carry flag on an add operation instead of performing a
> compare on a 64 bit value. The advantage to this is that it
> allows us to reduce the overall size of the call. On my Xeon
> E5 system the entire __phys_addr inline call consumes 30 bytes
> and 5 instructions. I also applied similar logic to the debug
> version of the function. My testing shows that the debug
> version of the function with this patch applied is slightly
> faster than the non-debug version without the patch.
>
> Finally, when building the kernel with the first two changes
> applied I saw build warnings about __START_KERNEL_map and
> PAGE_OFFSET constants not fitting in their type. In order to
> resolve the build warning I changed their type from UL to ULL.
>
> Signed-off-by: Alexander Duyck <alexander.h.du...@intel.com>
> ---
>
> arch/x86/include/asm/page_64_types.h | 16 ++++++++++++++--
> arch/x86/kernel/x8664_ksyms_64.c | 3 +++
> arch/x86/mm/physaddr.c | 20 ++++++++++++++------
> 3 files changed, 31 insertions(+), 8 deletions(-)
> +#ifdef CONFIG_DEBUG_VIRTUAL
> extern unsigned long __phys_addr(unsigned long);
> +#else
> +static inline unsigned long __phys_addr(unsigned long x)
> +{
> + unsigned long y = x - __START_KERNEL_map;
> +
> + /* use the carry flag to determine if x was < __START_KERNEL_map */
> + x = y + ((x > y) ? phys_base : (__START_KERNEL_map - PAGE_OFFSET));
> +
> + return x;
> +}
This is a rather frequently used primitive. By how much does
this patch increase a 'make defconfig' kernel's vmlinux, as
measured via 'size vmlinux'?
Thanks,
Ingo
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